This invention relates generally to piston-type internal-combustion engines such as diesel engines and more particularly to an assembly of a piston and connecting rod of improved construction.
The piston and its connecting rod of an internal-combustion engine of the instant piston type are subjected to repeated loads arising from the explosive pressure within the cylinder and from the inertia forces generated during the motions of the piston, its connecting rod, and associated parts and are thus placed under very severe conditions as considered from the viewpoint of mechanical stress.
In a typical known assembly of a piston and its connecting rod, these parts are connected by a wrist pin or piston pin fixed at its opposite ends to the side wall of the piston and pivotally connected at its middle part by way of a bearing metal sleeve to the small end or piston end of the connecting rod. As will be described more fully hereinafter, the end parts of the piston pin in this construction are subject to damage due to the forces mentioned above arising from the repeated explosions and inertia, particularly in high-performance engines. Another problem encountered in this typical piston and connecting rod construction is insufficient load bearing length of the piston pin for withstanding stress on its end parts and on its midportion caused by the above mentioned forces. This problem also will be considered more fully hereinafter.
In another piston and connecting rod construction known in the prior art, a concave spherical seat or socket is formed in the lower part of the piston and is coupled with a convex spherical ball formed at the upper or piston end of the connecting rod. Accordingly, the connecting rod during operation undergoes angular displacement about the centerline of the piston, whereby sticking of the piston rings and scuffing of the sliding surfaces are prevented. In this assembly, however, the concave spherical socket of the piston and the convex ball part of the connecting rod undergo mutual sliding movement while being in a state of direct frictional contact under high surface pressure. Moreover, the lubrication condition is poor. Consequently, the abrasive wear is severe, and seizure readily occurs.
Furthermore, the fabrication of the concave spherical socket and the ball of the connecting rod is troublesome. Even if a bearing were to be provided between these spherical parts, the fabrication of the bearing itself would be difficult, and it would further be difficult to machine the bearing metal of the bearing so that it would be in intimately close and complete contact with concave and convex spherical surfaces of the socket of the piston and ball of the connecting rod. If such an intimate contact cannot be attained, the bearing would be subjected to a repeated load due to the cylinder explosion pressure and inertia force. As a consequence, for example, fretting corrosion would occur between the spherical socket of the piston and the convex spherical surface of the bearing metal or between the concave spherical surface of the bearing metal and the ball surface of the connecting rod and may give rise to damaging of the piston.
To summarize, these piston and connecting rod coupling arrangements of the prior art are inadequate in reliability for engines of high output.